A communication system may use a plurality of frequency bands to transmit data over a corresponding plurality of channels, in a technique that may be referred to as frequency division multiplexing. For example, each frequency band may include a carrier frequency and the carriers may be separately modulated with data.
In such a system it may be desirable to drop the signal from one of the frequency bands, e.g., if it has reached its intended destination, and to add another signal in its place in the spectrum.
Thus, there is a need for a system for removing a signal in one of a plurality of frequency bands, and substituting another signal in the same frequency band.